Sister, Sister
by Emma and her Pet Unicorn
Summary: Jay and Will Halstead have a sister, the youngest and probably the most unpredictable of the family. When she decides to quit her job and go back to Chicago for good, she becomes involved with the Intelligence Unit, and not just because her brother is a cop. Turns out she's a damn good one too. But with Lucia-Marie Halstead comes unforeseen trouble. As usual.
1. Chapter 1

**this originally started as a one shot with two or three parts in my one-shots book (lots of Jay Whump and Halstead brotherly love if you care) and I got a few messages saying I should make it a book so..here we go!**

To say Lucy Halstead was pissed would be an understatement. The person at the desk saw her expression, and almost went for her gun, and if Lucy hadn't rolled her eyes and said her last name and purpose for her visit to the district, she probably would've 'politely' escorted her out. The youngest of the Halstead siblings had always had that look, the one that made people intrigued but wary, and not want to mess with her. The brunette marched up the stairs to the door that led to Intellligence, throwing it open after being buzzed in.

No one noticed her immediately and so she dropped her jacket onto the desk of her brother, loudly, and placed her hands on her hips. "I swear to god, I _will_ kill you if that ever happens again."

Everyone looked up, as did her brother, surprised and then looking even more surprised when he saw her glaring down at him. "Wait-"

Exasperated, she cut him off, waving her hands in the air to express her extreme frustration. "I had to take a cab! Do you know how many cases there are of people being kidnapped or killed during or after the cab ride?"

Erin Lindsay seemed worried, her eyes darting back and forth between the stare down. Hank Voight walked out of his office, followed by Antonio Dawson. Ruzek and Olinski were both smiling, seeming to recognize a banter between siblings.

"I mean, seriously? Did you two not even _consider_ that I could be dead right now? Because I could! Dismembered, beheaded, strangled-"

"Luce, you've been working too much, first of all, and second-"

 _"You were supposed to pick me up!"_

Jay's mouth opened and closed like a fish, trying to find something to say and finally decided upon, "Will was going to get you!"

" _Will_ called ahead and told me he had car crash victims coming in, which is convenient, and that he told you to come get me!" She took out her phone, unlocked it, showing him her texts with their oldest brother.

 **2:30, Will -**

 **Told J to pick you up, I'm stuck here. Huge crash. :-/**

 **2:30, Lucy -**

 **Okeydokey. ;-) go save lives**

He frowned and returned her phone, and Lucy cocked her hip. "So?"

"I...forgot..?" Jay tried to say, but she lightly punched him in the arm.

Erin decided to jump in right then, asking, "So, wait, you're his sister?"

The younger Halstead looked her up and down, her lips turning upwards ever so slightly, and she said, "That I am. You must be the partner that I've unfortunately heard very little about."

They shook hands, and Jay was getting nervous about two of the most important women in his life getting to know each other.

Lucy proceeded to meet the others in the Intelligence Unit, already about to launch into one of her stories about when she and her brothers were younger and left alone at their home for a few hours, the time that just about everything went wrong and the day Jay decided he would never go swimming again.

Then Platt walked into their space, saying, "You've a case straight from the chief. Body washed up on the dock shores, no limbs."

She stared at Lucy. "Ah, I forgot to mention, Halstead, you've got a visitor."

Jay bit his tongue to keep form letting out a disrespectful use of sarcasm. "Thanks, Sergeant." Erin said for him, placing a hand on his arm as a warning.

"Keys?" Lucy said, her palm out, waiting, Jay rolled his eyes and dug out his spare key to his apartment, which was thankfully large enough for a second person, now that Will had rented his own place too. He dropped them in her open hand with a small shake that made them jingle. She smiled, and went in for a hug. As the others were getting their things to go down to the crime scene, the two siblings held onto each other.

She didn't have to say anything to express herself.

"Missed you, too, sis," Jay said, into her soft brown hair, sincerely.


	2. Chapter 2

Hey, Luce! Over here," Will called from the bar, sitting on the stool with a drink in his hand. His brunette sister, whom he hadn't seen in person for a few months, spotted him and walked over. She pushed through a few men to get there, giving flirty smiles, and he refrained from rolling his eyes.

She plopped down next to him, gave the bartender a smile too, that was polite, and asked for a beer. Lucy sighed. "Car crash?"

He nodded. "I'm surprised I was even able to get out for a drink even though I'm still on call." He twirled his beer bottle around, cocked her head and looked at his sister. "So, why're you here?"

Lucy feigned being hurt. "What, not happy to see me?"

He gave her an unconvinced look. Suddenly, a loud beeping came from his phone, and he grabbed his jacket after reading the notification. Lucy watched him rush out, leaving his beer behind, with only a small apologetic wave in her direction. She checked her watch- Jay said he'd be there around 8:00, and it was five minutes past.

She took another sip of her drink, and was about to start taking to the girl behind the counter, with the dark hair and light brown skin. She seemed nice.

Someone sat down next to her. "Same as her, Gabby." Jay said, and was handed a cold beer by the girl, who smiled at him in response. "Thanks."

'Gabby' began to move to another customer, all the while wiping he counter with a damp towel.

"Are you going to ask?" Lucy questioned, after a few awkward moments of silence.

Jay acted innocent, glancing over at his fellow officers and shaking his head at their beckoning hands to go join them at their table. "About..."

She rolled her eyes and exasperatedly responded, "About why I'm back."

"Well, since you brought it up-"

"I quit my job."

He cuts his eyes at her. " _You did_ _**what**_?" He seemed incredulous; he couldn't believe this. He was partly relived, though. She traveled for her work a lot, went undercover, was assigned to dangerous cases and constantly moving from FBI related things to NCIS and CSI. But he was also feeling guilty. He'd always berated her on how she was the younger one, the baby of the family, that it was their job to look out for her. She was always out there on her own doing something stressful and hard and they weren't around to do that.

But she had loved what she did for a living. Lucy was young and smart, and she was more than good at police work. _Voight would like her._

And Jay and Will were happy for her.

Jay lightly slammed the bottom of his beer on the counter. "This seems to be a Halstead pattern. First Will, now you. Am I next?"

She looked nonchalant, like it was nothing, but he knew that she was obviously hiding the real reason behind what caused this sudden change. "I just...wanted to start a bit more fresh, y'know?"

"Uh huh." he said, and it didn't take a genius to see he was definitely not convinced. "Does Will know?"

"Not really." She smiled. "By the way, I took the guest room."

"Am I going to find empty chip bags and a shortage of food in my fridge when I get home?"

"Eh."

They held each other's gazes for a while, and the staring contest went on for a few seconds past a minute. Someone snapped their fingers in the middle of their faces and unfortunately for Lucy, she blinked first. Jay pumped his fist with a smirk. "Just a minute, Erin," he said, turning to look up at his partner, and then going back to staring at his sister. "Now you have to tell me one truth."

"Fine." Lucy grumbled, averting his eyes. It was a family thing- whoever lost the staring contest had to answer one question honestly. Jay almost always won. She only beat him when he was tired and annoyed.

"Why'd you come back? And are you staying for good, this time?" Jay asked, making it sound a bit like an interrogation.

Erin watched, almost amused, and still with the intention on getting some baby stories from the little sister she didn't know existed. Lucy seemed interesting. As soon as she'd spotted her walking into the intelligence unit, she had this deep down feeling of dread. If this girl was here for Jay, were they an item? It wouldn't be hard to believe. She was kind of...well, she wasn't ugly, and she had boobs. Usually, on any man, boobs worked. And then she saw the way they interacted, the way they argued- it was obvious that the two were family. She had no clue that her partner had a sister and a brother.

"That's two questions-"

"The second is mandatory-"

"I will-"

"Kill me? Sure."

Lucy huffed defiantly. "Jeez, fine. But let the record show that I know hundreds of creative ways to hide a body without anyone ever being able to prove I was the culprit."

"Okay, now answer the question, sis."

She rolled her eyes, but answered. "I got all up in someone's business while undercover and-"

"That's vague."

"Jesus Christ, Jay, fine." She took a large swig of beer, gulped it down, letting it go down roughly with a slight burning sensation blooming in her stomach. She whipped her head back towards him, her brown hair flipping to the side and falling down her back again. "You remember the techie guy, Christopher? Well, Chris got this Intel. I was back in forensics, and the Intel said that they needed a girl who was experienced to help out with this investigation. It seemed simple. It was all the same mumbo-jumbo about, like, possible criminals in some area."

She nodded a thanks at the man who gave her a second beer, taking another gulp.

"And?" Jay asked.

"I got shot." she said, straight faced.

His expression went slack. "You- you- _what_?"

The younger one began giggling and said in between each breath, "Kidding, kidding."

Jay clenched his jaw. "Continue the damn story, Lucia-Marie Halstead, and don't ever do that to me again."

"Sheesh, fine, chill." She rolled her eyes. "Anyway, I offered myself up with the gold crested resume and honours and all that stuff, and they almost immediately gave me the job. It was weird, which I should've known, but... I took it. I was tired of being cooped up in a lab with people who complained about police officers and FBI agents constantly demanding new evidence when they knew almost nothing about what they- well, sometimes me- do. So Chris hooked me up with some cool new X-23 wires, I hid them in my bra and had a spare in the lenses of my glasses, and I went in. Next thing I know, there's a girl bleeding out in front of me, and I've got a gun to my head, and the only thing I can think about is how I could die in Hollywood and not have seen my family or said goodbye in four months."

Her big brother tried to take this in stride.

It didn't work. "That is not the full story, Lucy, and what the hell happened during your undercover time?"

She grimaced, remembering something she wanted to forget, and said, "I came back because I want to stay in one place, Jay, and I can't keep moving around and about and not seeing my family for months on end, okay? I missed you guys."

And so he smiled, took his beer in one hand and her arm in the other, dragging her towards where Erin and the others were sitting.

"Guys, I believe you've already met my sister Lucia-Marie. She's going to be staying in Chicago for a while."


	3. Chapter 3

Lucia-Marie Halstead had always been a good girl to her parents, the fun one with her friends, and the don't-mess-with-me one with boys.

Only her siblings had ever seen every side of her.

But it had been a while since Jay had seen his 25 year old sister drunk as ever. This went to show that her story about why she was back in Chicago was not at all the whole truth, or even part of it. Lucy wasn't one to be too reckless in a bar.

He drove her back to his place, wincing as he opened the apartment door, worried of what he was going to see, with her leaning against him heavily. His eyes widened when he realized that the place was indeed not full of empty chip bags or glasses, or with the television still on and music playing loudly. In fact, it looked like she'd barely spent any time in there at all.

That thought was a bit worrisome, knowing his sister, but he ignored the gnawing feeling of dread and pushed her onto the couch lightly, locking the door behind him. He liked his place- it was a nice size, able to house two or three people, and in a nice building.

Lucy mumbled incoherently and he rolled his eyes, grabbing one of the many blankets available and putting it on top of her. She was asleep before he could even tell her goodnight as he made his way to his own bed.

The next morning, she woke up groggy and uncomfortable. Her head felt like someone was putting slight effort into hitting the inside of her skull with a hammer.

She stood up, pulling her messy hair into a ponytail to keep it out of the way, then made herself some coffee. At the last minute, she realized that maybe her brother would want some, so she made a second.

"'Morning." Jay's voice carried over to her.

"Your coffee's good." she said, handing him his mug and taking a careful sip from hers, calming her nerves.

He smirked. "I know."

She responded with a roll of her eyes and once again brought the mug of her own to her lips, taking a larger amount and swallowing it quickly, letting it burn her throat.

"So, Luce." Jay started.

"Uh oh..." she joked.

"What are you gonna do now? Get a job or something?"

"Jay..."

"Well, you can't just come here and not do anything for the rest of your stay. You're out of a job."

"Are you _trying_ to scare me off?" said Lucy, raining her eyebrows in inquiry. He stopped and pressed his lips into a thin line. "Okay, yes, I'm going to _try_ and find something. I could always be a bartender."

"You didn't graduate high school early and end up with the best genes for nothing."

"I know that. Maybe I'll work in a calmer division here. Like... Narcotics!" She snapped her fingers as if she'd just had the best idea.

Jay, on the other hand, looked instantly bored. "Narcotics? Seriously?"

A few moments of silence followed as she walked, barefoot, over to the table and sat down in the chair. She saw a copy of the case her brother was working on the counter as she walked by and glanced at it. "Hey, Jay," said Lucy.

"Yeah?" He was opening the fridge and looking for some eggs. When he didn't find anything he wanted to eat, Jay closed it and went to sit down across from her with his coffee and half a bagel, handing the other half to her.

"What's the case about? The one over there,"

He looked at the counter, the one she was pointing at. "Oh," Jay said. "We got a third decapitated body."

Lucy grimaced.

"What?" he asked.

"I hate serial killers." She shrugged.

An idea popped into his head. At least he could keep her busy while he was gone. "Here," he reached for the file and pulled it closer to the edge of the counter with his fingertips and then grabbed it before it fell off, placing it in front of her. "Take a look."

She did. As Lucy read over the information, the witness, which were little to non to speak of, and the evidence. "He's looking for attention, recognition." she said, flipping through a few of the photos. Jay watched her in slight fascination. He didn't get to see this side of her often because they never worked alongside each other. "Or maybe it's a girl..." She was frowning, and turned a certain picture around, facing him.

In it was a decapitated woman. "What makes you say that?" he asked.

Lucy pointed at the other pictures- all men, much cleaner and what seemed faster. "There's evidence of, you know, sexual intercourse, to say it the proper way. It's post-mortem. But with the woman, it looks more like she ended up in the wrong place at the wrong time. I have a feeling it's a female who is more into revenge. Maybe."

She pushed it back towards him and got up. Lucy put the empty mug in the sink, rinsing it quickly, and then went to the hallway that separated the bedrooms, disappearing into the one she had taken up as her own.

"Hey, do you need a ride?" Jay called, ten minutes or so later, twirling his keys on a finger as he, ready, waited at the door.

No answer.

"Luce?"

Still no answer.

So he quietly made his way to the door and lightly knocked. He realized it was ajar when he did so, causing it to open up more.

Lucy was shuffling around, surprised by him, and covering herself up quickly. Well, there wasn't much to cover up, actually. She was in a white tank top and skinny jeans.

Suspicion and that gnawing feeling in his gut returned, but he said nothing. "You need a ride?"

She nodded mutely.

Out of the corner of his eye, though, he saw her rubbing the back of her shoulder as he left the room.

-cpdcpdcpd-

When Jay told the others what he had found out about the killer, Voight squinted at him, sceptic. "Halstead, what source gave you this information?"

Jay hesitated.

"Halstead." Voight warned. Everyone was staring, intrigued, curiosity making the room tense. Erin nodded slightly, her notice for him to just tell Hank the truth already.

"Um, my...sister..." He trailed off slowly. Erin was raising her eyebrows and smirking. Something was obviously going on in her head, and he had to practically tear his gaze away from her face. _She looks nice today. No, Jay, stop thinking about her. And stop thinking about Lucia. Concentrate on not making your boss mad again._

"Your sister? So let me get this straight..." Hank walked up to him, making a big show of it, and grabbed the now-empty folder out of his hand. "You shared _confidential_ case files with your _baby_ _sister_?"

Halstead gulped and nodded. "That's, um, correct, sir." _Baby is kind of overdoing it._

Erin interrupted before Voight could say anything more, "Does she know what she's talking about?" She didn't seem all that interested in what's he was asking. Jay sent her a look of deep appreciation.

"Yeah." He didn't elaborate, and everyone seemed to get that he wasn't going to any time soon.

-cpdcpdcpd-

Lucy was out grocery shopping.

Mostly because she felt bored and if she was stuck doing nothing all day, she'd go nuts.

Normally, trying to find the right milk should be what rock bottom would look like for her. Unfortunately for her, she'd already seen and experienced rock bottom. It wasn't fun.

While humming some random song Lucy had most likely heard on the radio recently, she paid at the cash and took the bags of groceries to a taxi she'd called.

When she sat in the backseat, the driver asked, "Where to?"

"Uh."

She hadn't really planned out her day.

Like, at all.

So... "Chicago Med, please."

-cpdcpdcpd-

Jay didn't feel his phone buzz against his leg, in his pocket, until the fourth time Will texted him.

"Jay, just pick up the damn thing already. We can hear it from here." Ruzek said.

He didn't really want to, knowing it was either his sister or his brother.

Luckily, Erin saved him from doing so. "Guys! We found her. At some big-time bar and casino, looking for her next victim."


	4. Chapter 4

**I'm sorry the update took so long. Just so you know, things are about to start getting real interesting with our young Halstead girl- including a new job, which will not be in narcotics. *wink wink***

 **Pretty please leave comments/reviews/feedback and definitely suggestions. It's very motivational and also makes me feel really good. I honestly appreciate it a lot when I get emails and notifications saying someone left a review or favourited it.**

 **Enjoy! Thank you for sticking with this story, by the way!**

 **-the author**

It was safe to say that Lucia-Marie tended to run into trouble a lot. Which is why she had a black eye after going to the hospital, ironically. She went to have lunch with her eldest sibling, a doctor who worked in the emergency room as a trauma surgeon.

"The swelling's gone down considerably. And I don't have a concussion." she rolled her eyes, even though the outside of her left one was throbbing painfully. The freezing cold of the ice pack she had pressed against it was numbing.

Dr. Choi gave her a half smile and moved her hand and ice pack away from her face, squinting at it. "Well, I'm pretty sure Dr. Halstead wouldn't be thrilled with my decision to let you go."

"Boys. Don't they get that with some makeup, the bruising won't be all that noticeable?" she joked.

He chuckled lightly. "Fine, but I think he called you a ride."

Her spirits went down a bit. That ride was most likely Jay. "Damn it. He called in the cavalry."

She left the small examination room and took her hair out of its ponytail, trying to cover the dark bruising that had already started to develop on the left side of her face. That patient had steel fists, unfortunately for her.

"Remind me exactly how you were injured at a hospital?" her brother's voice carried it's way to her as he waited by the car, Erin in the driver's seat. She sent her a small wave and they smiled at each other.

"Will and I had a lunch date. I came to the ER to drag him to McDonald's, even though he's _convinced_ their food is poisonous..." She shrugged, "Honestly, I just wanted a milkshake."

Jay frowned at her, took a step forward and moved the hair out of her face. She swatted his hand away stubbornly. "It won't last more than a week." he said, even though he was still a bit annoyed.

"Anyway, some patient went berserk on this other patient and I happened to be right in the middle of them. I didn't move fast enough to get out of the way. Oh, and..." She pushed past him, handle already grasped in her hand. "I call shotgun!"

Erin choked on a laugh. Obviously her partner's manhood was at stake every time he needed to be in a car.

Jay clenched his jaw and took the backseat.

Then the girls started talking as if he weren't even there, which was halfway to interesting but still near annoying.

"Men are too complicated. They say we women have our own language-" Lucy started.

"And then they go around being more difficult than we are!" Erin finished.

The female Halstead pressed her head against the window, watching the streets go by as Erin drove. She closed her eyes, ready to have a short nap-

"-In pursuit of suspect in the murder cases right now, requesting backup immediately. We are currently in Freedom Park. She has a hostage and is in possession of a weapon-"

Erin stopped the car, looked at Jay behind her, who nodded, and then glanced at Lucy. Then she made an abrupt start toward a different direction. Pretty soon they had gotten to the park, where crowds of people had gathered behind the police officers. Lucy recognized the Intelligence members. One of them handed Jay a vest, and then tossed one to Erin. Lucy leaned back inside the car.

She knew what was coming.

"Stay here." her brother ordered, giving her a scolding look.

And there it was. The moment where he forgot about her own experience in these situations, where she was the little kid he had to protect.

"Uh-huh." she mumbled, rolling her eyes. The member who gave them the vests, Dawson, gave her a questioning look. He had probably seen the blooming black eye.

Then they rushed off, Jay heading towards a building, probably to act as a sniper. He was one of the best she'd ever met, although Lucy was required to support that fact since they were family.

She slumped in her seat.

Waited.

Waited.

 _Waited_...

"Screw it." She opened the dork and stepped out, moving in between the people who crowded around the scene, giving a wide berth to the officers.

Lucy stealthily made her way past the officers, who somehow didn't notice her slipping by and onto the scene itself. It looked like Erin was trying to talk her down, with her gun still drawn. The woman had a man in front of her, wild red hair a mess, eyes wide and screaming at them to get back. The man himself looked panicked, tense and shaking in her grasp, the gun against his head obviously unnerving.

"Halstead?" someone whisper yelled at her.

She glanced sideways at Olinski. "Yup."

"You're not supposed to be here."

"And _you're_ supposed to be paying attention to the scene, not little ol' me." she said, not even trying to hold back the snark. But he didn't seem to mind.

"Do you _know_ what's going on?"

"No offence, but it doesn't take someone with a high IQ to understand this." She looked to Erin, who saw her out of the corner of her eye. Lindsay was attempting to talk down the suspect calmly, but it was like things were only escalating from where they'd been a minute ago.

"You guys are doing it all wrong. He's going to get killed if you don't change tactics." she shook her head, biting her lip anxiously. She hated hostage situations, they were much too stressful for any human being.

"Okay, if this doesn't work, we- _who is_ _she_?" It was Voight, appearing next to Olinski and staring down at her with a scowl.

"This is-"

"Lucia-Marie Halstead. You probably don't remember me yelling at my brother the other day." She stuck out a hand, but he didn't even glance at it.

Voight glared at her. "How did you get over here? No, never mind. Just...get back _behind_ the line where you're not in danger of getting hurt, _please_." It sounded so tensely harsh coming from him that she almost wanted to laugh.

"Listen, I know I've already most likely pissed you off, but you're conducting this all wrong. This woman needs sympathy and understanding. There's a reason she murdered that woman with remorse and the men with hatred. It's-"

"You _read_ the damn _file_?" he ground out, clearly becoming angrier with her by the second. "I'm going to kill Jay. Civilians aren't allowed to know about-"

"Jesus Christ, what makes you think I'm a civilian?" she snapped. He looked so surprised that he dropped the scowl and instead stared at her, like he was trying to figure something out.

"Erin," he said loudly. Lindsay turned slightly towards him and he directed her to him. She walked over, not at all nervous with him, Lucy noticed. "Switch with little Halstead. Give her a vest, Alvin."

Lucy bit the inside of her cheek at what he'd referred to her as. She could get over it...later. "Uh. What?"

"You act like a cop. Unless-"

"No, I mean, yes. I am...a...cop." More like Special Agent, she thought. And more like was, she added in her head.

"And would Jay get mad about this?"

"Most definitely." She smirked.

He didn't seem to care. He handed her the vest, but didn't even get to make her put it on before she'd gone into the line of fire, standing a few feet away from the redheaded serial killer.

"Who are you?" Her words were rushed, pained, even.

"I'm Lucy. You?" Lucy had her hands in her pockets and could feel the silent thoughts and the people's eyes on her, the cops who were judging her ability. She tried to be relaxed.

Which is kind of hard to do when you're in this type of situation.

"Are you a cop?"

She cocked her head, looking thoughtful. "Not exactly."

"You're going to do the same thing, huh? Tell me to get my ducks in a row and stop?" She pressed the gun harder against the temple of the man.

"Let's forget about whoever you're threatening to kill right now and have a conversation."

"What is this? What are you doing?"

"Look, I'll even..." Lucy trailed off, showing the palms of her hands and then slowly ending down, retrieving the pocketknife she had in her converse and tossing it to the ground, then the black handgun she had in the back of her, tucked into her waistband. She showed it to the woman and then did the same thing with the weapon, hearing it land in the grass a foot or two away from her.

"Let's talk."

They both stared at each other for a few seconds.

Then, "Hannah Martinez. That's my name."

"Spanish?"

"...yeah."

"Cool."

Hannah seemed beyond perplexed at how relatively normal this conversation was. She, holding a gun to a person's head and surrounded by officers ready to shoot her, and Lucy, standing there so relaxed as if she were waiting in line for an ice cream.

"So what's the deal here? Why the men? And that poor girl. Revenge?"

And the normalcy disappeared.

"Why do you care?" she sneered in response. The safety of the gun could be heard being switched off.

"Woah, I'm just trying to understand what's going on."

"I...they were bad men." She looked uncomfortable.

Someone behind Lucy stepped forward to tell her something, in the middle of saying "This doesn't seem like a good idea-"

"Go back! Stay away!" Hannah was yelling, cutting in. Lucy pushed whoever it was back to his place and raised her hands in surrender.

"Hey, relax. He just wanted to make sure I was okay. So...the men? What made them so bad?"

"They were criminals and they got away with their crimes. They _deserved_ what they got. The girl..." She choked on her words. "I didn't mean to kill her." The last part came out quieter.

"I know."

"You- you do? How?"

"I just do. I believe you. But...him?" Lucy gave him a pointed look as his eyes darted around. "He didn't do anything. So at least let him go."

"I-I..." she trailed off, eyes darting to the floor. Ever so slowly, she let go of him, her hold of the gun also slipping until it almost dropped to the ground. He immediately ran to the officers at the side, nearest to him.

Before Lucy could react, though, Hannah Martinez had the gun pointed upwards, aiming for her jaw-

"Don't!" But it was too late. The loud bang of the shot surprised her and she stood frozen in place as she watched the blood pool around the dead body of a serial killer.


	5. Chapter 5

I am not going to apologize for the months, months and MONTHS of waiting you've all done because it's honestly not enough. Just so you know, the chapters further ahead are on Wattpad. Just look up Sister, Sister in the search bar and it should show up.

Also, I'll be coming back to edit this (you'll notice that like nothing is in italics as certain things should be.) so watch out for many more updates. You'll have at least six new chapters before Friday. (So the next two days.) this is a guarantee.

-Emma.

Sergeant Platt does not despise Detective Seymour.

In fact, she quite likes the young woman.

But either way, she needs to make it clear that she will not, will not, treat anyone differently.

Even if Detective Seymour was in desperate need of food.

"Oh come one, Sarge, please?" Seymour was saying. Her blonde hair was up in a ponytail, her shirt untucked and wrinkled. Behind her was her brother, asking to get going, beckoning for Platt to just say 'fine' instead of dragging it out.

"No." Platt shook her head.

"I'm desperate. Pllllleeeassse."

"Seymour, I already made it clear that I won't be giving you any of the pizza." To make the point, Platt took another piece out of the top box on the pile of recently-delivered pizza boxes. She slowly bit into the tip and ate it.

Lucy narrowed her eyes. She pivoted and left the station, her brother following.

"She'll get over it." Platt shrugged. Then she spit out the pizza. "Ugh. I don't even like that stuff. Is that onion...?"

 ** _About Two Months Ago_**

"Says here you beat a guy and he confessed." Voight said, his eyes still on the writing in her file. The unlocked, non-secret version, that is.

"Oh, yeah..." She winced.

He looked up. "What's the story behind it?"

"Well, there was this mute male teenager being accused of sexually assaulting a man's son, the man I got a bit...violent...with. He wouldn't talk, no matter what we said or did. Then when he turned up dead, the man had o choice but to let us talk to his son, who said that it was his father who was molesting him. I got pissed as it was, but when I learned that he was also the person who murdered the teenager...I went overboard." She played with her hands in her lap, worried he'd start pestering her about her work record.

Voight leaned forward. "From what I understand from your file, you work hard, you sympathize and understand, you profile and you're an early graduate. You've also conducted several successful undercover ops, which is something we could use as a skill. You're smart. Both on the streets and in general. But I can't have someone who won't get their hands dirty from time to time."

"Sir. I try not to lose control because all cases have a chance of hitting close to home. Sometimes I do get rough with the suspects or something, but I will not let myself go out of control. That case...it was really complicated. Some of them are. And those are the times that I get so angry that I just can't help but-"

"You're hired."

 ** _Present Time_**

"Operation New Apartment begins..." Jay checked his phone for the time. "Now."

"I can't wait to get out of your place." Her stomach grumbled. Boy, was she hungry. If only the desk sergeant had just given her one box. One damn box and she would've been fine. At this point she could eat an elephant. Her stomach was churning painfully.

"It's mutual, Luce, trust me."

Erin shook her head. "Jay, you could at least try and be nice about it."

He rolled his eyes. "I'm tired of having to make runs in the middle of the day to get her some damn tampons. I missed part of the hockey game three nights ago for that."

"At least she doesn't have serious mood swings." Erin mediated.

"She is right here!" Lucy exclaimed.

Jay shoved her playfully and led the way into the apartment building. Erin followed, but Lucy hung around back. She examined the exterior- traditional red brick, windows for every room, curtains mostly drawn. At least the neighbourhood was nearby to the station. Be positive. And stop thinking it smells like pot. She readied herself, shook her body out, and walked in.

"Okay, that's it. This place smells like drugs." she said, not able to hold back her breath anymore. Oops.

Erin glanced at her over her shoulder, taking a small whiff of the surrounding air. "Barely. All buildings around here smell like that."

"I'd rather not live in a place where there are routine drug busts."

"It's got no gangs, this neighbourhood's mostly clean, too-" Jay added.

"Mostly?" Lucy gaped. Dramatically, she stomped ahead of them up the stairs. "If you two like this place so much, why don't you move in together here?" Her voice bounced on the walls in the empty hallway. She heard someone yelling in one apartment and cringed at the sound of a door slamming.

Erin and Jay shared a look but didn't respond. Both of them were smirking slightly, though.

"Okay, apartment 13..." She jogged over to the door of the apartment. Before knocking, she turned to the other two. "I still think this place is a drug zone."

"Where are we with the gang case?" Ruzek asked, upstairs in the Intelligence unit's area.

"-you can't keep quizzing him on these things."

"Diego can't be keeping things like this from me!"

"Uh, guys?" Ruzek tried again. Antonio and Lucy were the only ones there. Olinski was nowhere to be found, to his annoyance, since he was his partner. The two partners were arguing about something, and he recalled the name 'Diego' as Antonio's son.

"He also needs to stay somewhere good in the food chain at school! If he rats out on people to his dad, the damn cop, then he'll be shunned or something! He needs to have a good rep-"

"I'm his father!"

"But they're also his friends!"

"I don't want him hanging around with some-"

"Some kids from a crappy neighbourhood? Who might have shit for parents?"

"I don't want him to hang around with kids who have free drugs around the house, that's all! And he won't listen-"

"At least he's not lying!"

"Guys!" Ruzek whistled loudly. Both turned to him, angrily. "Where the hell is everyone?"

Lucy looked around, shrugged. Antonio shook his head. Soon enough, the fire in their bodies dissipated and they had gone back to looking nonchalant. Both sat down, the only female in the room placing her shoes on the desk, ignoring the ringing of her cellphone.

Eventually, though, the third time the phone rang, she took it out. "If he doesn't stop calling me, I'm going to smash it." She answered, a disgruntled look taking over. "What now?"

Her expression didn't change. "No. I'm not coming back just to-" She visibly bit the inside of her cheek. "No. Now stop calling me."

"Same guy?" Dawson questioned, reading over the gang paperwork.

She nodded mutely, tossing the phone onto the desk. "I was in a good mood."

"Well, your mood's about to get worse." someone said, walking into the middle of the room.

"Al! You're back!" Ruzek said, sounding very relieved. He jumped out of his seat and rushed forward. "What've we got?and where is everyone?"

"We were near the back, talking to Cameron." He sounded tired, exhausted even. "A hit was out out on our dead guy. The girl was a prostitute that worked for them and they were in a relationship, and she was there, wrong place and wrong time. Cameron is a dealer for the Locitos (pronounced LO-CHEE-TOS) and he was supposed to be the one who retaliated. Wouldn't say who put out the hit."

Antonio and Lucy made a big show of fist bumping, and both yelled, "We called it!"

Ruzek rolled his eyes. "So where is everyone now? Still at the cage?"

Alvin nodded. "Voight said that he's going with Antonio to the gym where the gang usually hangs out, going to talk to the other and find out who ordered the hit, so we can know how they found out and who killed their members."

Lucy gaped. "What? But Dawson's mine. I don't share partners, Al."

"What Voight says goes."

Lucy made a pouting face, but then sighed. She placed a hand on Antonio's shoulder. "No matter what happens, you're still my best friend and favourite partner ever."

"Oh, cut the dramatics Seymour. You'll get him back." Ruzek rolled his eyes. She silently flipped him the finger when no one was looking.

a/n: I didn't think this particular case through very much so it's possible it seems mega rushed and stuff, but I've got the next few cases all planned out. Well, the case itself, not how it'll work out lol.


	6. Chapter 6

Lucy was at Antonio's gym at 6:00 AM that day, practically murdering the dummy, her current opponent. She didn't feel a sliver of remorse, seeing as it was not a real person, but either way...

It was sure to bruise by evening.

"Luce! Come on!" Jay yelled.

She turned her head in his direction, all the while adding two lazy punches to the chest of the dummy. She walked over to her brother, who stood by the desk.

"I get that you're really enjoying the discount and everything, but we should get going. Also..." Jay leaned to the side to look at the dummy. "I think your enemy has been vanquished." he added in a posh-like voice.

Mid-unwrapping of her knuckles, Lucy shoved him playfully to the side. They walked to the changing rooms, and she ran in to pick up her gym bag, a black Adidas one, and then exited, pulling on a cardigan as they left. It was a bit chilly out, but pretty good for October.

"So..." Jay started the car, and she sat down in the passenger seat. Lucy began putting her long blonde hair (longer than she thought it ought to be, and she thinks she should cut it short in a bit) in a bun.

"I hate it when you start your sentences with 'so'. It's like breaking up with someone."

Jay raised his eyebrows, still looking at the road. "You're my sister, not my girlfriend."

"Yeah, I don't think I could _ever_ live up to Erin's standards. She set the bar a bit too high." Lucy said sarcastically. Although, she had to admit that she had come to really like Erin.

" _Anyway_. What happened to your shoulder?" He said it quickly, like it'd be less confrontational. Like ripping off a band aid. It hadn't been the first time he'd noticed the three white scars, which were normally covered by a shirt. But today, she must've forgotten about it when she put on her gym clothes.

Lucy acted nonchalant. "Huh? Oh. Nothing that I know of." A subconscious stifling occurred then, like a ghost was putting ice cold fingers on her shoulder's skin, tracing the thin yet prominent lines. She ignored the goosebumps that she could feel on her arms. "Probably from a fender bender or something. You and I both remember my amazing collegiate background," she laughed halfheartedly.

"Uh-huh." Jay was obviously not convinced, but neither one said anything more for the rest of the ride to the station.

"Hey, Dawson." Jay called. Lucy had already gone to change out of the exercise leggings and put on what he was assuming we're going to be jeans.

"Yeah?" Antonio asked, following the older Halstead into a more discreet location.

"Lucy's been acting weird for the past two months and it's been driving me nuts...so I was hoping you could try and dig into what made her come here."

"Wow, no beating around the bush, huh?"

"Listen, man. She's my sister, and I know she's keeping something important from me. Actually, more than _one_ something."

Antonio nodded, clapping him on the back reassuringly. "I got a little sister too, Halstead, so I get it. I'll try, okay?"

"They found Toby Wilkins." Voight said, and those words made everybody quiet down. The grim, mildly disturbed expression on their sergeant's face only worsened how Intelligence felt.

"He's dead, isn't he?" Ruzek spoke up.

Antonio gripped the side of his desk, his jaw locked into place.

"Strangled." Voight's gravelly voice seemed to bring them all away from their reverie, and everyone began putting on their jackets.

"You okay?" Lucy whispered to Dawson as they left.

"Yeah." Antonio sighed. "I hope the son of a bitch who killed him winds up dead."

"I'll be sure to let you have a moment or two with him alone. As long as I don't have to hide a body."

They were at the black undercover police car, Lucy snatching the keys from Antonio and getting into the driver's side. She hated being at the side of things, unless she needed a nap of course. Naps were great.

During the drive, Lucy noticed how incredibly...fidgety her partner was. She didn't ask about how weird he was acting, but she noted in her head to do so at some point.

She made a sharp turn at a corner and parked abruptly. Both detectives got out of the car and hurriedly joined the others. Pushing through the swarm of people taking videos and photos with their cellphones, past the news journalists, away from the crying father and mother who stood by the crime scene tape.

As soon as she saw the suitcase and the clothed boy stuffed inside, Lucy stopped. Her mind had already stopped thinking as someone on the scene and gone to thinking like an analyst or profiler. She was taking in the scene without emotions getting involved.

"What do you think?" Voight was standing beside her now, same with Olinski. They watched her expectantly.

"Let me get a better look." she said, moving closer and kneeling.

Eleven year old Toby Wilkins was dead, put into a suitcase after being strangled. She wasn't an ME, but anyone could tell the boy had been beaten during the three days he was missing. It was revolting.

"You'd have to check, but I don't think he was sexually abused." said Lucy as she looked a this face- eyes closed, hands clasped.

Had his hair been brushed? And he looked...clean, almost.

"The person who took him could be female, but the way he was just put into a suitcase and left here..." She stood, turned around in a full circle. The crowd had grown, people whispering, staring.

"We need to get them to clear the area." Olinski suggested, already moving towards the parents and other uniformed officers. She grabbed his arm and continued to survey the area.

"No. If this was done by a female, it could be a concerned motherly type who showed up to know the turnout, if the boy's body is going to be properly taken care of. I think."

"You're saying that she could be here?" While Olinski sounded alarmed, calculating, she was calm and collected. Her eyes swept over the crowd, mainly looking for the concerned looking females. She took out her phone and began to video tape the whole crowd, moving around to include everyone who was gathered at the scene.

"I'm saying that any one of these people could be the kidnapper."

"No one turned up in the database." Mouse said, swivelling his chair from one side to the other, looking bored. He was frowning at the computer screen. Jay nodded in thanks.

"Damn." he muttered to himself when he reached his desk. Erin was sitting on the edge of it, writing something down on a piece of paper and passing it to him discreetly. Her eyes went to Lucy first, then to him, and finally pointedly to the paper she'd given him.

He read it,

 _What's going on with you two?_

He gave her a, _I'll tell you later_ type of look. She nodded, but looked slightly conflicted.

"Kim!" Lucy called out in the locker room, seeing Burgess changing out of what seemed to be a stained white top into a blue blouse.

Kim looked up, spotting the slim blonde walking towards her. She had a hold of Erin Lindsay's wrist, latched on with an iron grip. Erin looked downright confused.

"You both need a night out. Form the short time I've been working alongside you women, I've realized once again that this boys club needs to stop controlling our every move which means..." She smiled. "We. Need. A-"

"Don't say it..." Erin groaned.

" _Girls night!_ " Lucy exclaimed enthusiastically.

Burgess, despite the sore muscles caused by an encounter with a rough-and-tumble type of purse-snatcher, nodded. "I need one of those. So I'm totally in."

They both turned to Erin. Lucy had released the grip she'd had on her fellow detective's wrist and was watching her expectantly, almost threatening her with her expression if she said she wouldn't go.

Erin sighed. "Okay," she replied in defeat.

Lucy clapped her hands together with (very) exaggerated enthusiasm. "See you two at the bar after work!"

Antonio and Lucy stepped on the 'welcome' mat of the home. People were inside, talking, crying, some were even yelling. Mrs. Wilkins opened the door, her posture delicately straight. Her short and curly brown hair was a mess, like she'd just woken up. The long robe she wore was wrapped tightly around her, like armour.

They made eye contact, she and Antonio, and the detective's were then quietly led into the home. Relatives eyed them I the way to the kitchen, and they all sat at the kitchen table.

"We're so sorry-" Lucy started her typical apology meant for grieving people.

Mrs. Wilkins held a hand up in a 'stop' motion. "I know. I've been hearing it all day. Just..." She sighed, wiping her eyes. "Ask away. I'm free all day, after all." It was a bitter comment.

"We will be as quick as we can." Lucy assured her. Antonio stood from the table, taking looks at the pictures of a young brunette girl and her little brother, eleven year old Toby. Others with teachers and groups of students after a school play or other type of even, a class photo, et cetera.

"I-I read that most child abductions are done by someone who knows the abducted child. I made... A list. Of family friends who knew Tobias well." Mrs. Wilkins pulled out a paper form her pocket with shaking hands. Antonio sat down again, and gently took the paper out of her hands, which were grasping it tightly.

"That's really helpful. Thank you." he said.

She cut her eyes at him. "Do you have kids?"

He nodded.

"Then...then you understand that this is..." Furiously, she used her sleeve to wipe her eyes, leaving blotchy red marks around her eyes.

Dawson nodded again. "I know. We just want to find whoever did this to your son."

Mrs. Wilkins hiccuped and stood, going to the sink. She took a glass, turned on the tap, and filled it with water. Then she sat down again, taking a few sips of water and then deep breaths.

"My husband is at the shooting range, I think." she said, staring at the patterns in the table. "When we got home, I fell asleep late and he's been out since then."

Antonio and Lucy shared a look. She was stuck in her own grief.

"Ma'am," Lucy tried again.

"You look young to be a detective. Really young. What do your parents think? You're so...young..." Mrs. Wilkins rambled. She had bags under her eyes.

"I graduated early from high school and went to the FBI Academy, Mrs. Wilkins." Somehow, that seemed to pull the grieving mother out of her reverie.

"Is there anyone that Toby was close with?" Antonio asked.

During the time that he was asking questions, being careful with how he phrased them and refilling her water glass regularly, Lucy thought of Toby. He was stuffed into that suitcase, dead. He wasn't shot, no, but he seemed to have been beaten to death. Bruising covered his small body, trauma to his head. But he wasn't assaulted before that, and the way he was taken care of- hair washed, body scrubbed of any dirt, he was fed daily since the eve of his disappearance...almost...motherly-

"Mrs. Wilkins," she blurted, like the puzzle pieces clicked together. Antonio and the woman looked at her, as if she'd just appeared. "Do you know any women under forty who lost children? Who knew Tobias well?"

She had a blank look on her face, thinking about it. "Under forty?" she asked with uncertainty.

"Yes. Under forty." Lucy said, seeing the different stages of confusion and thought flit over Mrs. Wilkins' expression.

And then she watched as the woman's mouth moved, realization dawning. And the words came out, along with a name.

Antonio felt very conflicted. He sat in the passenger seat of the car, having finished telling Voight what they'd learnt, and remembering what Jay had asked of him to do. It wasn't exactly his business what his partner's history was with the FBI, and all things related, but then again, she was his partner. They had to trust each other.

So... "Hey, Lou?" He used the nickname they'd gotten used to. She glanced at him quickly, turning the car onto another street and slowing down for the stop sign.

"Uh-huh?"

"Why don't you ever, um, talk about the FBI?"

She blinked. "'Cause. It was the past and I prefer to live in the present. That's why."

That was the end of what could've been a discussion, but after all, Antonio knew when to stop asking questions from her. It wasn't like he'd never asked before then. He just never had more than pure curiosity as a reason to do so.

_  
"Karen Quinn!" Ruzek yelled as he, Jay, Erin and Olinski busted through the front door, guns out and vests on. They split up, all going in different directions to find their main suspect.

"Over here!" Ruzek's voice floated through the house, coming from the backyard. "She's running!"

He tackled her, unceremoniously, and brought them both to the ground, feet away from the open backyard gate.

"Karen Quinn-" he said, taking out the handcuffs and putting them on the struggling redheaded female. "You're under arrest for the kidnapping and murder of Tobias Wilkins."

She sat there, sweaty hands clasped together, in the interrogation room.

The detectives were all watching her from the other side of the glass. "Guess we won't be roughing her up, huh?" Ruzek commented, looking like he was contemplating the idea.

Lucy gave him a sideways look. "Why not?"

All the other detectives of Intelligence stared at her like it was obvious, as if she were a complete idiot.

Slowly, she came to realize the difference between the woman, _woman_ specifically, and the men they'd roughed up in the past. Lucy frowned, almost disappointed about it. "That's stupid. I've been roughed up plenty of times. And I'm a female." The rest came out faltered and in a grumble.

At the prospect that she'd been ' _roughed up_ ' before, the others already had questions they were dying to ask. But she was already opening the door to the interrogation room, sitting down at the table and spreading out the papers of the case file. Calmly, Lucy clasped her hands together.

"And this is where the magic comes in." Antonio whispered to the others.

Lucy swept her eyes up and down, examining the woman across form her. _She looks pretty anxious._

"Do you know why you're here?" Lucy asked.

Karen Gillan slowly shook her head, almost like she was calculating what was going on in her head.

"Someone murdered a young boy name Tobias Wilkins who was beaten to death and then stuffed into a suitcase by someone who didn't give a flying shit about him. And that _someone_ was you." But before Karen could protest,may anything, express herself in any way, Lucy continued. "But first you kidnapped a child who trusted you. Made his parents suffer through the possibility of him never being found, and then the loss of their baby boy." She leaned back in her chair. "There's nothing you can do now, Karen."

The redheaded female in the small room watched as Lucy's seemingly cool glare turned into one of indifference. "You're just another kidnapper turned murderer who didn't give a shit about-"

"No!" Karen interrupted, her eyes wide. "I-" she faltered, and ran her hands over her face and to the back of her head, flattening her hair down. "I _cared_. I swear that I did. He just..." She sniffed. "Toby was the best one in my class. All the other students always...always _picked_ on him. Like they did with Amanda...with Mandy."

"Your daughter?" Lucy asked, eyes still hard as ice and still looking like she didn't actually give a damn about what was going on. "Karen, she and him were two different children. Amanda is dead."

Karen shivered. "I know. _I know that._ "

"So tell me what happened. You got angry with Toby, right? And you hit him and then you _just_ _couldn't_ _stop_..." (Behind the glass, on the outside, Jay nearly flinched at how...natural...she sounded. Like it wasn't the first time she'd had to turn into this cold hearted, indifferent human being who just didn't care at all.)

Karen shook her had vigorously, red curls flying from side to side. Her green eyes were wild. "That's not what happened. Toby tried to...he tried to leave..." She hit the table with her fist, and Lucy was surprised by the sudden burst of annoyance from the suspect. "I told him _not to do that_. And I got mad, and I yelled, and I ran after him, and he...he... He _fell_."

"What do you mean, he fell?" Lucy demanded.

"Down the stairs. And he was gone. Just-just like my other baby. My Mandy."

Lucy stood from her chair and tossed a note pad onto the table, even though she had decided to record the interrogation beforehand. "Write it down."

She left the room and as soon as the door slammed shut behind her, leaving behind the sobbing young woman, Lucy grinned victoriously. "We got her." And even though she hated these types of cases, the ones where children died or were kidnapped or where widowed mothers look for new sons or daughters, this was a victory. In some odd way, it made her happy.

It was the end to the sad tale of Toby Wilkins.

Later that night, Lucy and the others were at the bar, just enjoying a few drinks and talking about some old cases. "So, Ruzek..." She looked at him with curiosity. "You gonna get the nerve up to win Kim back?"

He offered a bittersweet smile. "Nah, not now at least."

She sipped her beer and then pointed a finger at him. "You'd better get your ducks in a row, man. She's worth it. Besides...I kind of liked you two together anyway."

Ruzek chuckled. "Thanks for the advice, Seymour, but what do you know about marriage? I don't see a ring."

She smirked, an ' _I know something you don't know and probably will never know about'_ type of look on her face.

At the counter, Herrmann had served a small late of simple fries to both Antonio Dawson and Jay Halstead. "Sorry, Halstead." Antonio apologized. "I didn't really press further. I'd rather she was covering my back on the job instead of trying to kill me."

Jay shrugged. "It's fine. I'll just have to work this crap out myself."

Erin, on the other hand, who had just sat down, thought differently. "From what I know about Lucy since I've met her, she's not going to put up with you snooping in her personal life. She'll get pissed if you pursue, Jay."

"It's kind of a big brother thing, Lindsay." Antonio defended.

"Would you like your sibling poking around in everything you did that they don't know about? Maybe she went through something she doesn't want to reveal just yet." Erin shook her head, like she couldn't believe this was a discussion. Sure, it definitely peaked her instincts that something was up with her fellow female detective at Intelligence, that the whole story was not even _near_ to the one she told Jay the first night she was back in Chicago.

But digging deeper could have consequences and repercussion. It could get someone hurt.

 **3459 words-**

 **Next chapter:**

 _ **Detectives Lindsay and Seymour go undercover, Jay asks Mouse to look up his sister's medical records and finds more than he thought he would, and Antonio (much to the happiness of his partner) enters a relationship with the girl Lucy set him up with.**_


End file.
